A typical prior art disk drive system 10 using perpendicular recording is illustrated in FIG. 1. In operation the magnetic transducer (head) 14 is supported by the suspension (not shown) as it flies above the rotating disk 16. The magnetic transducer 14, usually called a “head” or “slider,” is composed of elements that perform the task of reading and writing magnetic transitions. In a disk drive using perpendicular recording the recording head is designed to direct magnetic flux through the recording layer in a direction which is perpendicular to the plane of the disk. Typically the disk 16 for perpendicular recording has thin films 21 including a hard magnetic recording layer 28 and a magnetically soft underlayer 29. During recording operations using a single-pole type head, magnetic flux is directed from the main pole of the recording head perpendicularly through the hard magnetic recording layer, then into the plane of the soft underlayer and back to the return pole in the recording head. The shape and size of the main pole and any shields are the primary factors in determining the track width. The write head portion (not shown) of head 14 uses pole piece 42.
U.S. Pat. No. 6,531,202 to Litvinov, et al. is an example of a magnetic recording medium for perpendicular or vertical recording. The medium includes a magnetically soft underlayer deposited on the substrate. Suitable soft magnetic materials are said to include CoFe and alloys thereof, FeAIN, NiFe, CoZrNb and FeTaN, with CoFe and FeAIN being preferred soft materials. A magnetically hard recording layer is deposited on the soft underlayer. Suitable hard magnetic materials for the recording layer are said to include multilayers of Co/Pd or Co/Pt, L10 phases of CoPt, FePt, CoPd and FePd and hcp Co alloys, with such multilayers and L10 phases being preferred hard materials.
In U.S. Pat. No. 6,524,730 to Ga-Lane Chen a soft magnetic underlayer for vertical recording is referred as “keeper layer”. The soft underlayer is said to give better writing efficiency by pulling the magnetic flux down from the writing pole of a head of the magnetic recording medium. Examples given of soft magnetic materials are NiFe, CoZrNb, FeAINx.
Bulk tetragonal L10 ordered phase materials (also called CuAu (I) materials), such as CoPt and FePt, are known for their high magnetocrystalline anisotropy and magnetic moment, properties that are also desirable for high-density magnetic recording media. The C-axis of the L10 phase is similar to the C-axis of hcp CoPt alloys in that both are the easy axis of magnetization. Thus, while the disordered face-centered-cubic (fcc) solid solution of Co and Pt has cubic symmetry and low magnetic anisotropy, the ordered L10 phase has uniaxial anisotropy similar to, but greater in magnitude than, hcp CoPt alloys. U.S. Pat. No. 6,007,623 to Thiele, et al., describes a method for producing a horizontal magnetic recording medium that has as its magnetic film a granular film with grains of a chemically-ordered FePt or FePtX (or CoPt or CoPtX) alloy in the tetragonal L10 structure. These granular films reveal a very high magnetocrystalline anisotropy within the individual grains. The film is produced by sputtering from a single alloy target or co-sputtering from several targets. The granular structure and the chemical ordering are controlled by means of sputter parameters, e.g., temperature and deposition rate, and by the use of an etched seed layer that provides a structure for the subsequently sputter-deposited granular magnetic film. The structure of the seed layer is obtained by sputter etching, plasma etching, ion irradiation, or laser irradiation. The magnetic properties, i.e., Hc and areal moment density Mrt, are controlled by the granularity (grain size and grain distribution), the degree of chemical ordering, and the addition of one or more nonmagnetic materials, such as Cr, Ag, Cu, Ta, or B. These nonmagnetic materials are partly incorporated into the grains, but mainly accumulate at the grain boundaries. The role of the nonmagnetic material is thus to “dilute” the magnetization and to decouple the magnetic exchange between the grains.
The use of SiO2 with CoPtCr to enhance grain boundary formation without disrupting the epitaxy in perpendicular magnetic recording media has been described. (T. Oikawa, et al., “Microstructure and Magnetic Recording Properties of CoPtCr—SiO2 Perpendicular Recording Media”, IEEE Transactions on Magnetics, vol. 38, no. Sep. 5, 2002, pp. 1976-1978.)
Tilted magnetic recording is one of the leading candidate technologies for extending hard disk drive (HDD) areal density to beyond one Tb/in2 and data rates beyond one Gb/s. What is needed is a manufacturable way to make high SNR media with an anisotropy direction approximately 45 degrees out of the plane of the disk surface. The head structure and basic media fabrication methods for perpendicular recording can be used with tilted media. Tilted recording devices can be expected to cost about the same as currently available technologies. Tilted recording has a number of benefits over perpendicular recording. First, the anisotropy field and magnetization of the medium can both be approximately doubled (to around Hk 30 kOe and Ms=800 emu/cc) since the grains are easier to reverse for a given maximum head field. The fourfold increase in energy density means a fourfold reduction in grain volume without thermal stability problems. Second, switching field variations due to the distribution in anisotropy angle are up to 10 times smaller for tilted recording. This results in much sharper bit transitions and higher bit density. Third, the guard band between tracks is much smaller for tilted recording because the switching field and energy barrier increase for the larger write field angles at the track edge. Fourth, tilted recording is capable of much higher data rates than perpendicular recording since the reversal torque is much higher. Switching times up to ten times shorter than for perpendicular recording have been reported.
Gao and Bertram have proposed using a soft underlayer with a magnetic layer with 45 degree anisotropy tilted out of the plane of the disk in conjunction with single pole heads. The anisotropy orientation can be cross-track, down-track or randomly distributed. In their theoretical paper, Gao and Bertram do not give materials or techniques for producing the hypothetical media which they analyze. (Kai-Zhong Gao and H. Neal Bertram, “Magnetic Recording Configuration for Densities Beyond 1 Tb/in2 and Data Rates Beyond 1 Gb/s”, IEEE Transactions on Magnetics, vol. 38, no. 6, November 2002, pp. 3675-3683.)
The use of MgO(111) underlayer to improve the crystallographic orientation of L10 FePt(111) films has been discussed by Jae-Yoon Jeong, et al. The FePt was deposited at a temperature of 300° C. and then annealed 400°-500° C. for one hour. (Jae-Yoon Jeong, et al., “Controlling the Crystallographic Orientation in Ultrathin L10FePt (111) Films on MgO(111) Underlayer,” IEEE Transactions on Magnetics, vol. 37, no. 4, July 2001, pp. 1268-1270.